El Niño Wants a Warm Winter. The Polar Vortex Has Other Ideas.

A super El Niño is going to go up against the polar vortex this winter, but who will come out on top more often? Forecasters are predicting that the two influential factors will often be at odds, driving alternating periods of unseasonable warmth mixed with frigid temperatures.

Clash of El Niño and the Polar Vortex

It has been well documented that a potent El Niño could be the major driver of the weather this winter. Earlier in the month, the National Oceanic and Atmospheric Administration's (NOAA) Climate Prediction Center (CPC) confirmed that El Niño was continuing to strengthen.

The recurring climate pattern has over a 90% chance of becoming a "very strong" event during the fall and winter season. The CPC went on to say that there was a 75% that the upcoming El Niño has a 75% chance of becoming a historic event that rivals previous phases beginning in October.

While this climate phase typically brings warmer temperatures to the northern half of the country, the polar vortex may also have something to say about this. During last month's update, the CPC said that “with an event of this magnitude, the chances of experiencing impacts consistent with El Niño are larger, though not guaranteed.”

The polar vortex is a massive area of cold air and low pressure that hovers over the Earth's poles. The vortex over the North Pole intensifies during the winter months, frequently expanding and pushing the bitterly cold air to the south into Canada and the U.S.  

The stratospheric polar vortex generally begins to come together in late August and early September, persisting over the North Pole until it begins to fall apart in May. The vortex frequently weakens at times during winter, allowing the cold air to slip farther south. This weakening is often responsible for the cold snaps that plague the U.S.

El Niño Forecast to be in the Driver's Seat

While the polar vortex certainly has the ability to impact the winter weather in the U.S., this year's El Niño paired with the Pacific Decadal Oscillation pattern is likely to be the dominant influence. In general, a strong stratospheric polar vortex usually translates to warmer-than-average temperatures throughout the Northern Hemisphere. However, that does not mean that outbreaks of frigid air can be ruled out.

The polar vortex is most likely to combine with the strong El Niño during the back half of the winter. A weakening vortex in late January and February could override the influence of El Niño, resulting in temperatures that land colder than average across the northern half of the U.S.

The bottom line is that while the polar vortex will likely trigger brief intrusions of unusually cold air this winter, it will still be El Niño that drives the overall weather pattern in the months ahead.

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